This application is based on Patent Application No. HEI 9-150721 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical quantity measuring method or an optical quantity measuring apparatus for measuring optical quantity of an image on an image bearing member formed by using an array of image forming elements, such as PLZT light shutter array, LED array, an array of heat generating elements, or an array of ink drop expelling elements.
2. Description of the Related Art
Heretofore, various types of optical recording devices have been proposed which switch optical signal generating elements ON/OFF to form an image (latent image) on a photosensitive member. As to the photosensitive member, the electrophotographic photosensitive member, and the film or printing paper using a silver salt sensitive member are known. Known optical signal generating elements include optical shutter elements which switch ON/OFF the light emitted from a light source in accordance with an applied voltage, and LED elements which themselves generate light in accordance with an applied voltage. Well known optical shutter elements include elements formed of PLZT material, liquid crystal elements and the like. This type of optical recording device is constructed with a plurality of optical signal generating elements arranged in an array-like layout, and is referred to as a solid-state scanning-type optical recording device. This type of solid-state scanning-type optical recording device is constructed so as to allow adjustment (e.g., by modulation of the drive signal pulse width or voltage, changing the pulse train combination and the like) of the light quantity of each optical signal by measuring the amount of light of each optical signal generating element and correcting the amount of light of each element in accordance with the measured value.
Japanese Laid-Open Patent Application No. SHO 61-150286 discloses a light quantity measuring method for measuring the light quantity of optical signal generating elements for the purpose of correcting said light quantity. This publication discloses a construction providing a plurality of LED elements arrayed in the main scan direction, and discloses a method of measuring the amount of light of optical signals emitted by said LED elements by sequentially turning ON said LED elements in the main scan direction and detecting the amount of light emitted by each said LED element via a photodetector. The LED array extends in the main scan direction, and has markedly different lengths between the length from an LED element positioned at the center of the array to the photodetector, and the length from the LED element positioned at the ends of the array to the photodetector. Therefore, the photodetector detects the amount of light of the optical signals from the various LED elements under different distance conditions, thereby preventing high precision detection of the light quantity.
Another method considers moving the photodetector along the main scan direction and sequentially turning ON each LED element synchronously with said movement, but the LED element scanning speed and sensor moving speed must be accurately synchronized. The starting position of the photodetector must be finely adjusted. Thus, an encoder and precision moving mechanism are required, thereby greatly increasing the cost of the actinograph. Corrections with the device incorporated in an image forming apparatus were not conducted.
Methods of sequentially turning ON each optical signal generating element are disadvantageous in that the influence of light leakage from adjacent optical signal generating elements is not reflected in the measurement, and image irregularities are not adequately eliminated when reproducing solid images. Although consideration has been given to switching ON a plurality of optical signal generating elements simultaneously, the problem of identifying the position (addressing) of each optical signal generating element remains.
Other than optical signal generating elements, heat generating elements used in a thermal printer and ink drop expelling elements used in an ink jet printer also require similar correction to compensate irregularities among these elements.
A principal object of the present invention is to provide an improved optical quantity measuring apparatus or method. Another object of the present invention is to provide an optical quantity measuring apparatus or method capable of correcting the irregularities among image forming elements. Still further object of the present invention is to provide an optical quantity measuring apparatus or method capable of correcting the irregularities among image forming elements via a simple operation or simple construction.
To achieve at least one of the above mentioned objects, one aspect of the present invention essentially comprises (1) forming an image on an image bearing member by using an array of light signal emitting elements which are aligned in a first direction; and (2) sensing the intensity of the image by a photosensor with relatively moving the image bearing member to the photosensor in a direction which is orthogonal to a direction corresponding to the first direction. By relatively moving the image bearing member in the second direction, the photosensor successively senses portions of the image corresponding the light signal generating elements. The image may include first part for identifying positions of the light signal generating elements with respect to the first direction and second part for evaluating light quantities emitted from the light signal generating elements. The photosensor may include a first photosensing element for sensing the first part and a second photosensing element for sensing the second part.
The above identified aspect may be reflected in a method for measuring quantity of light emitted from an array of light signal generating arranged in a first direction, and in a measuring apparatus for measuring quantity of light emitted from an array of light signal generating arranged in a first direction.